Based on my own reading of IQ and general heuristics I've developed from observing people (i.e. this is my folk wisdom, I am not sharing links), on a team of SDEs, the one SDE who is really really sharp, not just due to tenure, but generally just grasps things faster and earns the intellectual respect of his peers, is probably about 8-15 points higher than the average IQ of the SDEs around. Again, this is super heuristic, as IQ is non-linear.